1. Field of the Invention
The present invention relates to x-ray scanning devices, and in particular to such devices having an x-ray source disposed on one side of a conveyor for generating a fan-shaped x-ray beam at objects on the conveyor and having a detector array on the opposite side of the conveyor for receiving the radiation passing through the conveyor and the objects thereon.
2. Description of the Prior Art
X-ray scanning devices for examining objects moving through an x-ray beam on a conveyor or other type of transport device having electronic circuitry for acquiring and processing signals received by a detector array and displaying the resulting image on a display unit are known in the art. Generally, the processing circuitry includes an image storage memory which employs one memory cell for each detector within the array, and also includes a scanning device for the detector array which supplies detector signals to the image storage memory.
X-ray examination devices of this type are used, for example, for examining baggage. The objects to be examined are moved past the detector array, generally in the form of a detector line or row, which is disposed in a plane perpendicular to the direction of conveyance of the objects. The objects are moved on the conveyor with a specific speed.
Because of the line or row structure of the detector array, the material or objects to be examined are scanned in strips. After converting to a digital signal, the samples, the number of which depends upon the number of detectors, are either evaluated in real time or are entered into a memory in order to construct a video image.
The imaging scale M on the display unit, as viewed in the running or conveying direction, is a function of the scan rate A and of the running speed V of the object or material to be examined, and can be calculated according to the following relationship: EQU M=A/V.times.K
In the above equation, K is a system constant which, for example, accounts for image format and pixel size.
In practice, the requirement that the conveying device have variable speed is often necessary in order to enable optimum matching to the examination or production sequence in which the device is being used. This can be done in combination with an x-ray scanning device only when changes in the scale in the running direction were accepted as well.